People have been doing fanscans of new WSJ series before even viz's online service, some groups start translating whatever they think looks interesting and sometimes those are successes, sometimes they're flops.
One thing that happens sometimes is a group will start doing a new series, getting excited and the manga getting some english popularity, but then they drop it or make it very low priority upon realising it'll get cancelled. If you look back at new series before Viz started their Jump Start service, you'll see that most batches have at least one series with full english scans (sometimes started as it released, sometimes people went back to translate it after it ended). You can't really base popularity on what gets translated (especially) since all a series needs is for one person to be a fan and want to practice their Japanese skills.
Back around the time I started reading manga Lock-on! of all things was getting translated and I doubt many people even remember that (I remember when it suddenly ended I was a bit confused since I knew nothing about the manga industry and had never read a cancelled series before).
Even going back to hit series popularity doesn't necessarily mean translations, Otokojuku has full english scans and barely anyone's even heard of that in the west outside of J-stars. Meanwhile everyone knows Bobobobobobobo, the anime was even localised, yet it's only now about to have a complete english scan done.
